<?php
/**
 * Zend Framework
 *
 * LICENSE
 *
 * This source file is subject to the new BSD license that is bundled
 * with this package in the file LICENSE.txt.
 * It is also available through the world-wide-web at this URL:
 * http://framework.zend.com/license/new-bsd
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to license@zend.com so we can send you a copy immediately.
 *
 * @category   Zend
 * @package    Zend_Crypt
 * @subpackage DiffieHellman
 * @copyright  Copyright (c) 2005-2009 Zend Technologies USA Inc. (http://www.zend.com)
 * @license    http://framework.zend.com/license/new-bsd     New BSD License
 * @version    $Id: DiffieHellman.php 16971 2009-07-22 18:05:45Z mikaelkael $
 */

/**
 * PHP implementation of the Diffie-Hellman public key encryption algorithm.
 * Allows two unassociated parties to establish a joint shared secret key
 * to be used in encrypting subsequent communications.
 *
 * @category   Zend
 * @package    Zend_Crypt
 * @copyright  Copyright (c) 2005-2009 Zend Technologies USA Inc. (http://www.zend.com)
 * @license    http://framework.zend.com/license/new-bsd     New BSD License
 */
class Zend_Crypt_DiffieHellman
{

	/**
	 * Static flag to select whether to use PHP5.3's openssl extension
	 * if available.
	 *
	 * @var boolean
	 */
	public static $useOpenssl = true;

	/**
	 * Default large prime number; required by the algorithm.
	 *
	 * @var string
	 */
	private $_prime = null;

	/**
	 * The default generator number. This number must be greater than 0 but
	 * less than the prime number set.
	 *
	 * @var string
	 */
	private $_generator = null;

	/**
	 * A private number set by the local user. It's optional and will
	 * be generated if not set.
	 *
	 * @var string
	 */
	private $_privateKey = null;

	/**
	 * BigInteger support object courtesy of Zend_Crypt_Math
	 *
	 * @var Zend_Crypt_Math_BigInteger
	 */
	private $_math = null;

	/**
	 * The public key generated by this instance after calling generateKeys().
	 *
	 * @var string
	 */
	private $_publicKey = null;

	/**
	 * The shared secret key resulting from a completed Diffie Hellman
	 * exchange
	 *
	 * @var string
	 */
	private $_secretKey = null;

	/**
	 * Constants
	 */
	const BINARY = 'binary';
	const NUMBER = 'number';
	const BTWOC  = 'btwoc';

	/**
	 * Constructor; if set construct the object using the parameter array to
	 * set values for Prime, Generator and Private.
	 * If a Private Key is not set, one will be generated at random.
	 *
	 * @param string $prime
	 * @param string $generator
	 * @param string $privateKey
	 * @param string $privateKeyType
	 * @return void
	 */
	public function __construct($prime, $generator, $privateKey = null, $privateKeyType = self::NUMBER)
	{
		$this->setPrime($prime);
		$this->setGenerator($generator);
		if (!is_null($privateKey)) {
			$this->setPrivateKey($privateKey, $privateKeyType);
		}
		$this->setBigIntegerMath();
	}

	/**
	 * Generate own public key. If a private number has not already been
	 * set, one will be generated at this stage.
	 *
	 * @return Zend_Crypt_DiffieHellman
	 */
	public function generateKeys()
	{
		if (function_exists('openssl_dh_compute_key') && self::$useOpenssl !== false) {
			$details = array();
			$details['p'] = $this->getPrime();
			$details['g'] = $this->getGenerator();
			if ($this->hasPrivateKey()) {
				$details['priv_key'] = $this->getPrivateKey();
			}
			$opensslKeyResource = openssl_pkey_new( array('dh' => $details) );
			$data = openssl_pkey_get_details($opensslKeyResource);
			$this->setPrivateKey($data['dh']['priv_key'], self::BINARY);
			$this->setPublicKey($data['dh']['pub_key'], self::BINARY);
		} else {
			// Private key is lazy generated in the absence of PHP 5.3's ext/openssl
			$publicKey = $this->_math->powmod($this->getGenerator(), $this->getPrivateKey(), $this->getPrime());
			$this->setPublicKey($publicKey);
		}
		return $this;
	}

	/**
	 * Setter for the value of the public number
	 *
	 * @param string $number
	 * @param string $type
	 * @return Zend_Crypt_DiffieHellman
	 */
	public function setPublicKey($number, $type = self::NUMBER)
	{
		if ($type == self::BINARY) {
			$number = $this->_math->fromBinary($number);
		}
		if (!preg_match("/^\d+$/", $number)) {
			require_once('Zend/Crypt/DiffieHellman/Exception.php');
			throw new Zend_Crypt_DiffieHellman_Exception('invalid parameter; not a positive natural number');
		}
		$this->_publicKey = (string) $number;
		return $this;
	}

	/**
	 * Returns own public key for communication to the second party to this
	 * transaction.
	 *
	 * @param string $type
	 * @return string
	 */
	public function getPublicKey($type = self::NUMBER)
	{
		if (is_null($this->_publicKey)) {
			require_once 'Zend/Crypt/DiffieHellman/Exception.php';
			throw new Zend_Crypt_DiffieHellman_Exception('A public key has not yet been generated using a prior call to generateKeys()');
		}
		if ($type == self::BINARY) {
			return $this->_math->toBinary($this->_publicKey);
		} elseif ($type == self::BTWOC) {
			return $this->_math->btwoc($this->_math->toBinary($this->_publicKey));
		}
		return $this->_publicKey;
	}

	/**
	 * Compute the shared secret key based on the public key received from the
	 * the second party to this transaction. This should agree to the secret
	 * key the second party computes on our own public key.
	 * Once in agreement, the key is known to only to both parties.
	 * By default, the function expects the public key to be in binary form
	 * which is the typical format when being transmitted.
	 *
	 * If you need the binary form of the shared secret key, call
	 * getSharedSecretKey() with the optional parameter for Binary output.
	 *
	 * @param string $publicKey
	 * @param string $type
	 * @return mixed
	 */
	public function computeSecretKey($publicKey, $type = self::NUMBER, $output = self::NUMBER)
	{
		if ($type == self::BINARY) {
			$publicKey = $this->_math->fromBinary($publicKey);
		}
		if (!preg_match("/^\d+$/", $publicKey)) {
			require_once('Zend/Crypt/DiffieHellman/Exception.php');
			throw new Zend_Crypt_DiffieHellman_Exception('invalid parameter; not a positive natural number');
		}
		if (function_exists('openssl_dh_compute_key') && self::$useOpenssl !== false) {
			$this->_secretKey = openssl_dh_compute_key($publicKey, $this->getPublicKey());
		} else {
			$this->_secretKey = $this->_math->powmod($publicKey, $this->getPrivateKey(), $this->getPrime());
		}
		return $this->getSharedSecretKey($output);
	}

	/**
	 * Return the computed shared secret key from the DiffieHellman transaction
	 *
	 * @param string $type
	 * @return string
	 */
	public function getSharedSecretKey($type = self::NUMBER)
	{
		if (!isset($this->_secretKey)) {
			require_once('Zend/Crypt/DiffieHellman/Exception.php');
			throw new Zend_Crypt_DiffieHellman_Exception('A secret key has not yet been computed; call computeSecretKey()');
		}
		if ($type == self::BINARY) {
			return $this->_math->toBinary($this->_secretKey);
		} elseif ($type == self::BTWOC) {
			return $this->_math->btwoc($this->_math->toBinary($this->_secretKey));
		}
		return $this->_secretKey;
	}

	/**
	 * Setter for the value of the prime number
	 *
	 * @param string $number
	 * @return Zend_Crypt_DiffieHellman
	 */
	public function setPrime($number)
	{
		if (!preg_match("/^\d+$/", $number) || $number < 11) {
			require_once('Zend/Crypt/DiffieHellman/Exception.php');
			throw new Zend_Crypt_DiffieHellman_Exception('invalid parameter; not a positive natural number or too small: should be a large natural number prime');
		}
		$this->_prime = (string) $number;
		return $this;
	}

	/**
	 * Getter for the value of the prime number
	 *
	 * @return string
	 */
	public function getPrime()
	{
		if (!isset($this->_prime)) {
			require_once('Zend/Crypt/DiffieHellman/Exception.php');
			throw new Zend_Crypt_DiffieHellman_Exception('No prime number has been set');
		}
		return $this->_prime;
	}


	/**
	 * Setter for the value of the generator number
	 *
	 * @param string $number
	 * @return Zend_Crypt_DiffieHellman
	 */
	public function setGenerator($number)
	{
		if (!preg_match("/^\d+$/", $number) || $number < 2) {
			require_once('Zend/Crypt/DiffieHellman/Exception.php');
			throw new Zend_Crypt_DiffieHellman_Exception('invalid parameter; not a positive natural number greater than 1');
		}
		$this->_generator = (string) $number;
		return $this;
	}

	/**
	 * Getter for the value of the generator number
	 *
	 * @return string
	 */
	public function getGenerator()
	{
		if (!isset($this->_generator)) {
			require_once('Zend/Crypt/DiffieHellman/Exception.php');
			throw new Zend_Crypt_DiffieHellman_Exception('No generator number has been set');
		}
		return $this->_generator;
	}

	/**
	 * Setter for the value of the private number
	 *
	 * @param string $number
	 * @param string $type
	 * @return Zend_Crypt_DiffieHellman
	 */
	public function setPrivateKey($number, $type = self::NUMBER)
	{
		if ($type == self::BINARY) {
			$number = $this->_math->fromBinary($number);
		}
		if (!preg_match("/^\d+$/", $number)) {
			require_once('Zend/Crypt/DiffieHellman/Exception.php');
			throw new Zend_Crypt_DiffieHellman_Exception('invalid parameter; not a positive natural number');
		}
		$this->_privateKey = (string) $number;
		return $this;
	}

	/**
	 * Getter for the value of the private number
	 *
	 * @param string $type
	 * @return string
	 */
	public function getPrivateKey($type = self::NUMBER)
	{
		if (!$this->hasPrivateKey()) {
			$this->setPrivateKey($this->_generatePrivateKey());
		}
		if ($type == self::BINARY) {
			return $this->_math->toBinary($this->_privateKey);
		} elseif ($type == self::BTWOC) {
			return $this->_math->btwoc($this->_math->toBinary($this->_privateKey));
		}
		return $this->_privateKey;
	}

	/**
	 * Check whether a private key currently exists.
	 *
	 * @return boolean
	 */
	public function hasPrivateKey()
	{
		return isset($this->_privateKey);
	}

	/**
	 * Setter to pass an extension parameter which is used to create
	 * a specific BigInteger instance for a specific extension type.
	 * Allows manual setting of the class in case of an extension
	 * problem or bug.
	 *
	 * @param string $extension
	 * @return void
	 */
	public function setBigIntegerMath($extension = null)
	{
		/**
		 * @see Zend_Crypt_Math
		 */
		require_once 'Zend/Crypt/Math.php';
		$this->_math = new Zend_Crypt_Math($extension);
	}

	/**
	 * In the event a private number/key has not been set by the user,
	 * or generated by ext/openssl, a best attempt will be made to
	 * generate a random key. Having a random number generator installed
	 * on linux/bsd is highly recommended! The alternative is not recommended
	 * for production unless without any other option.
	 *
	 * @return string
	 */
	protected function _generatePrivateKey()
	{
		$rand = $this->_math->rand($this->getGenerator(), $this->getPrime());
		return $rand;
	}

}